The present invention relates to suspension systems having telescoping tubular elements and mechanisms for adjusting the relative telescopic movement of the tubular elements. More particularly, the present invention relates to compact, lightweight bicycle suspension systems having a spring preload adjuster, and/or a hydraulic lockout device that may be selectively, manually engaged to substantially prevent operation of the suspension system.
Vehicles, and bicycles in particular, have been provided with suspension systems for cushioning impacts or vibrations experienced by the rider when the vehicle contacts bumps, ruts, rocks, pot holes, or other obstacles in the path along which the vehicle is being ridden. Typically, bicycle suspension systems have been configured for use in the front or rear bicycle fork, in the head tube that connects the front fork to the bicycle frame and handlebars, in the seat post, and in conjunction with a rear wheel swing-arm assembly, as well as in other locations. When configured for use in a front fork, the suspension system has two pairs of telescoping tubular elements (an inner tubular element and an outer tubular element) forming the left and right legs of the fork. A resilient biasing element, such as a spring, biases the tubular elements apart. The tubular elements are said to undergo a compression stroke when the elements telescope together (the inner element slides into the outer element), such as upon impact to the fork. The tubular elements are said to undergo an expansion stroke (or rebound stroke) when the elements telescope apart (the inner element slides out from the outer element), such as after a compression stroke or upon riding over a rut. The biasing element absorbs energy imparted to the fork during compression, and releases the stored energy during rebound of the fork.
Various features have been added to such suspension systems in order to suit the needs of a variety of users. One such feature is the ability to adjust the preload on the biasing element in the bicycle suspension fork. Among other things, the preload on the compression spring determines the "sag" for the fork, that is, how much the fork initially compresses when a rider sits on the bicycle. If the fork does not sag at all, the fork will be inadequately responsive to variations in road conditions. For example, if the fork has no sag, it cannot expand to meet the road when the bicycle rides over a rut or other depression in the rider's path. On the other hand, if too much sag is present in the fork, the fork may bottom-out too easily (i.e., the inner tubular element may move excessively into the outer tubular element, resulting in collision of the elements).
Although bicycle suspension systems have generally experienced considerable commercial success in connection with bicycles designed for predominantly off-road use, such as bicycles known as "mountain bikes," such systems have not experienced the same success in connection with bicycles not intended for off-road use, such as bicycles known as "road bikes." One common reason is that suspension systems add weight to road bikes which is particularly undesirable given the high desire for lightweight bicycles for long biking excursions for which road bikes are often used. However, the benefits suspension systems confer on mountain bikes would nonetheless also be desirable for road bikes.
Due to the nature of their use, road bikes typically do not experience the same variety of obstacles or harshness of impacts as typically experienced by mountain bikes. Unlike the typical mountain bike, however, the typical road bike has thin, high profile tires that provide little impact absorption. Thus, impacts that would be virtually unnoticed by a mountain bike rider may cause discomfort to road bikers. Indeed, during long-distance riding, such as commonly done with road bikes, irregularities in the rider's path and vibrations caused from such irregularities will likely disturb and fatigue the road bike rider. Such fatigue may effect the rider long before the rider would otherwise be fatigued from the mere exertion necessary for simple riding of the bicycle over the long distance.
Several problems are inherent in designing suspension systems for bicycles such as road bikes. For example, because weight is of critical concern to road bike riders, and particularly to road bike racers, a suspension system must be lightweight, while still providing adequate adjustment capabilities. In addition, the system must be compact so that it may be aerodynamically packaged in the bicycle, and its adjustment mechanisms must be easy to use. Because bicycle weight is a central concern to bicycle riders, particularly road bike riders and racers, any preload adjustment mechanism should also be as lightweight as possible. Of course, it is also desirable that the adjustment mechanism be easy to manufacture and easy to use.
Another crucial consideration for road bikers is conservation of energy. When a rider is sprinting or climbing, for example, the rider will often lift himself or herself out of the bike seat while pedaling, causing the road bike suspension system to oscillate. The suspension system thereby absorbs a portion of the rider's power output, a result which is highly undesirable.